Cloning and expression of the human p8, a nuclear protein with mitogenic activity.

We have previously identified a new rat mRNA, provisionally named p8, which showed a strong, but transient, induction in the pancreas in response to acute pancreatitis. We report here the cloning and sequencing of the human p8 cDNA. The human p8 polypeptide is 82 amino acids long and shows an overall identity of 74% with the rat counterpart. The complete structure of the p8 gene was also established. The p8 gene comprises three exons separated by two introns and the gene was mapped to chromosome 16. Analysis of the p8 primary structure suggested the presence of a bipartite motif of nuclear targeting, indicating that p8 may function within the nucleus. This presumption has been confirmed by transfection of COS-7 cells with the p8 cDNA followed by immunostaining with specific antibodies. p8 mRNA expression is induced in some, but not all, cells by serum starvation and ceramide. To analyze the p8 function, we stably transfected HeLa cells with a p8 expression plasmid, and measured their growth and their sensitivity to apoptosis. Response to TNF alpha and staurosporine-induced apoptosis was not modified by p8 expression. However, cells expressing p8 grew significantly more rapidly.